The instant invention relates to systems and methods for triggering the deployment or actuation of vehicular safety devices and, more particularly, to a prediction-based system and method which anticipates conditions requiring such deployment or actuation of the safety devices to provide superior response thereto.
A variety of systems for actuating vehicular safety devices are well known in the art. Such systems are used to sense a crash condition and, in response to such a condition, to actuate an air bag, or lock a seat belt, or actuate a pretensioner for a seat belt retractor. Typically, the safety device is actuated or deployed into its protective position when an impact exceeding a predetermined magnitude is detected by the actuating system.
One prior art method for crash detection integrates the output of an electronic acceleration sensor over time and compares the result against a time-varying threshold velocity. A major drawback of this method is its need for determining when to start running the time-varying threshold, i.e., when the reference time for the time-varying threshold is to be reset to zero time. Another problem associated with the integration method of crash detection is that crash severity cannot be determined early enough for high-speed angular, partial barrier, or pole crashes. Moreover, the wide "grey area" between "fire" and "no-fire" conditions for low-speed crash conditions often results in an inadvertent deployment of the safety device when deployment is unnecessary, or nondeployment of the safety device when deployment is necessary.
Still further, raw velocity is not a particularly good measure of the effect of a crash on the human body. One criterion often employed with the integration method is the "5 inch--30 msec" rule, which states that an air bag should fire 30 msec prior to the time in which the passenger to be protected thereby will have moved 5 inches. Unfortunately, the passenger may well move forward 5 inches during a normal vehicle braking pattern--a condition in which air bag deployment would not only be undesirable but extremely hazardous.
Other prior art methods for assessing crash severity attempt to deemphasize the use of simple velocity calculations and instead calculate values for vehicle "jerk," i.e., the slope of the acceleration data; or the energy dissipated during a crash. Unfortunately, experience has shown that jerk alone is incapable of properly discriminating between conditions requiring actuation of a vehicle safety device and conditions where such actuation is either unnecessary or undesirable. Moreover, the "energy method" continues to utilize velocity information, resulting in the same types of deployment problems and slow response times as are encountered with the integration method. Additionally, the energy method is further limited in that it is accurate only over short time intervals.